1. Technical Field of the Invention
This invention relates generally to concrete support structures and in particular, to stay-in-place forms (i.e., composite shells) for forming concrete support structures.
2. Description of the Related Art
Concrete columns are commonly used as upright supports for superstructures. Bridge supports, freeway overpass supports, building structural supports and parking structure supports are just a few of the many uses for concrete columns. Other concrete support members such as beams, walls, slabs, girders, struts, braces, etc. are employed to impart strength and stability to a large variety of structures. These concrete support structures exist in a wide variety of shapes. Typically, these concrete support structures have circular, square or rectangular cross-sections. However, numerous other cross-sectional shapes have been used including regular polygonal shapes and irregular cross-sections. The size of the concrete support structures also varies greatly depending upon the intended use. Concrete columns with diameters on the order of 2 to 20 feet and lengths of well over 50 feet are commonly used as bridge or overpass supports.
Conventionally, some concrete columns have been constructed by filling a cylindrical form having a network of rebar mounted therein with a concrete composition, allowing the composition to cure, and removing the form.
Also, in the past, elongate paper fiber tubes have been used to form concrete columns. The tubes are made by spirally winding several layers of strong fiber paper. The spirally wound paper is laminated along its seams with a special adhesive. The outside of the tube can be coated with hot wax for protection against adverse weather conditions. Concrete is poured into the tube and allowed to harden so as to form a column. After hardening, the tube is stripped away from the concrete column and scrapped.
Rather than paper tubes, reusable steel or wood forms can also be used. Concrete is poured into these forms and allowed to harden. After hardening, the form is removed from the concrete structure and can be used again.
All of these conventional concrete support structures are subject to deterioration of their long-term durability and integrity. Permeability of the exposed concrete by water can cause the concrete to deteriorate over time. When moisture is trapped in the concrete and freezes, cracks typically form in the concrete structural members. In addition, some of these conventional concrete support structures are located in earthquake prone areas but do not have adequate metal reinforcement or structural design to withstand high degrees of asymmetric loading.
More recently, composites have been used to repair and retrofit columns, beams, walls, tanks, chimneys and other structural elements. However, a need exists to use composites in a prefabricated form to strengthen new constructions, protect internal reinforcing steel, provide fiber reinforcement outside of a concrete layer, to provide better appearance features, and to solve the above problems.